The seven murderers, rapist and thieves on the run in Texas are armed and angry  and, law enforcement sources admit, as rare as they are vicious.

"I have never heard of seven people escaping -- or five people or three people -- and staying together for even 24 hours, let alone several weeks," says Dennis Slocumb of the International Police Association, who hunted down fugitives for the Los Angeles County Sheriff's Department for 32 years.

Normally, Slocumb says, cons don't run far or for very long. But the Texas Seven have broken all the rules.

"What surprises me the most is that they have appeared to stay together through out this time," he says. "And that also makes them incredibly dangerous."

Nationwide, an estimated 10,000 inmates escape from prison every year. The escapees usually follow a similar pattern.

"There's a lot of escapees," claims Rick Kulp of John Jay College. "The U.S. Justice Department estimates about 2% of all felons escape at some point."

One of the largest prison breaks on record occurred in California, when 14 inmates escaped in 1995. Most were back behind bars within hours, reports CBS News Correspondent Byron Pitts.

The infamous James Earl Ray -- the man who assassinated Martin Luther King Jr. -- escaped once, but eventually died in prison.

There have also been bizarre breakouts, like the inmate in Maryland who dug himself out of prison with a spoon  twice

But Kulp says there has never been a case like the one in Texas.

"Most of them are resolved relatively quickly and relatively peacefully," he says, acknowledging that the seven in Texas have been on the run for a long time. "Sure that worries me. I think it worries anybody that desperate people are on the loose."

And it is desperation of the worst kind: The seven convicts are now facing the death penalty for killing a police officer Christmas Eve.

No one in law enforcement knows when they'll find them, and no believes they'll surrender peacefully.